Conventionally, a method of cutting vegetables to be eaten raw into predetermined sizes and transporting or selling them has been carried out. This method is carried out when vegetables for salad to be eaten raw are cut into predetermined sizes, are divided into small pieces for single persons, are packed and are sold, or vegetables cut in a processing plant are transported to related restaurants. In recent years, the demand tends to increase. Besides, needs for a treatment of enabling the long preservation of grains, tubers, or seeds or nuts, or a treatment of performing washing and sterilization when they are processed as food, are also increased.
Particularly, for vegetables to be eaten raw, such as salad vegetables, washing is performed and a sterilization treatment is performed in order to prevent a change in quality or decomposition until they are eaten. For this, there is also a method in which a washing step by clean water and a sterilization step using a chemical agent are independently performed in separate work places. However, recently, as a rational method in which such washing and sterilization are performed at the same time, a method of using ozonized water is proposed. As this method, there is a revolving current method disclosed in Japanese Patent Laid-Open No. 19376/1997. That is, this is a method in which stored water in a washing tank into which vegetables are put is circulated by a circulation pump to generate a revolving current in the washing tank, and an ozone-containing gas generated by an ozone generator is blown into the washing tank. By this, bacteria stuck on the vegetables are sterilized, and at the same time, pollutants such as agricultural chemicals are also removed, and moisture is supplied to cells of the vegetables to revive freshness. As another method, there is a method disclosed in Japanese Patent Laid-Open No. 290049/1999. In this method, after vegetables are received in a space of a sealed type chamber, low concentration ozonized water is poured to such a degree that the vegetables are not soaked. Stored ozonized water is circulated and jetted to the vegetables. By this, washing and sterilization of the vegetables are performed under a mixture atmosphere of gaseous ozone and ozonized water.
In the conventional methods, first, in the revolving current method disclosed in Japanese Patent Laid-Open No. 19376/1997, even if air containing ozone is blown into the washing tank, before the ozone dissolves, most of it passes through the washing tank without stopping and is diffused into the atmosphere. Thus, there has been a problem in a sterilization effect by ozone.
On the other hand, in the method disclosed in Japanese Patent Laid-Open No. 290049/1999, the ozonized water is water stored in the sealed container, and this stored water is cyclically used as wash water. As compared with the former, although an improvement in the sterilization effect by ozone can be expected, gradual contamination of the wash water can not be avoided. Thus, after washing by the ozonized water, it is necessary to perform a step of, for example, performing washing by clear water such as tap water,
Further, since both are of a batch type in which vegetables are put into the container and are washed, they are unsuitable methods as a continuous method applied to an apparatus for continuously washing plenty of vegetables.
In view of such circumstances, the invention has an object to provide a method in which a large amount of food materials can be always continuously washed and sterilized by fresh ozonized water, and which uses a small quantity of water and is economical.